Different Endings
Here's how to unlock the different endings:

Ending #1 "Beyond Time": 
     Deafeat Lavos after reviving Crono at Death Peak.

Ending #10 "Dino age": 
     Deafeat Lavos after facing Magus, but before facing Azala.

Ending #11 "What The Prophet Seeks": 
     Deafeat Lavos after facing Azala, but before Schala opens 
     the sealed door.

Ending #12 "Memory lane": 
     Deafeat Lavos after Schala opens the sealed door, but before 
     restoring the light to the pendant.

Ending #13 "Dream's Epilogue": 
     Defeat the Dream Devourer beyond Time's Eclipse

Ending #2 "Reunion": 
     Deafeat Lavos while Crono is dead.

Ending #3 "The Dream Project": 
     Deafeat Lavos in the Oceab Palace or immediately upon starting 
     a new game +.

Ending #4 "The successor of Guardia": 
     Deafeat Lavos after saving Leene and Marle, but before visiting 
     the End of Time.

Ending #5 "Good Night": 
     Deafeat Lavos after visiting the End of Time, but before returning 
     to the Middle ages.

Ending #6 "The Legendary Hero": 
     Deafeat Lavos after arriving in the middle ages, but before 
     obtaining the Hero's Badge.
     
Ending #7 "The Unknown Past": 
     Deafeat Lavos after obtaining the Hero's Badge, but before 
     the Gate key is stolen.

Ending #8 "People of the times": 
     Deafeat Lavos after regaining the gate jey, but before giving 
     the Masamune to Frog.

Ending #9 "The Oath": 
     Deafeat Lavos after giving the Masamune to Frog but before 
fighting Magus.



New Dungeon: Dimensional Vortex
     This  new  dungeon has three parts to it and can only be unlocked
when  you've completed the game by defeating Lavos at the end of Black
Omen.

Dimensional Vortex: Beat the game by taking the Black Omen path.


New Game+
     Defeat Lavos and obtain any of the 12 original endings.

Lost Sanctum
     The  Lost  Sanctum  is one of the new bonus dungeons added to the
DS.  In order to unlock this, you must unlock the Black Omen in 12,000
B.C.  The  Lost  Sanctum  will  apear  in 65 Million BC, and 600 AD in
certain locations.

Infinite Strength Capsules
     When  on  the  black  omen,  you  will come across a Blubber Hulk
(which  at  first looks like a tornado on the ground). Approach it and
have Ayla use Charm which gives you the strength capsule. Run away and
go  back  through  the  door  you  came through (with the two Nus) and
repeat.

Unlimited Shelters
     Go to Guardia Forest in 600 AD. Once inside, take the first right
and go to the upper path. While in the small clearing, you'll notice a
bush  in  the  upper  left.  Go  next to the bush and it will begin to
shake.  Press  A  and  a monster will pop out, leaving a Shelter as he
runs  away. Get the Shelter, and then leave the forest and reenter. Do
this until you have as many shelters as you want.